The prior art teaches a method of forming a shape of an article by casting a slip of silicon metal particles suspended in a vehicle into a porous mold. The porosity of the mold permits the vehicle of the slip to flow out of the mold leaving behind a compacted mass of silicon metal particles. The compacted particles are dried and removed from the mold to produce a shape formed of closely packed silicon metal particles. This shape is a green body of silicon metal particles having a very low level of strength. The green body is placed in a furnace and treated at high temperatures with nitrogen gas to produce a final article of silicon nitride having substantial strength.
Difficulty has been encountered in moving the green body from the molding step to the nitriding step. Since the green body lacks any substantial strength, it is easily damaged.
It is an object of this invention to provide a method of nitriding a slip cast article such that the mold in which the article is formed also forms a support for the article during drying, transfer, and nitriding. It is a further object of this invention to provide a method of forming a silicon nitride article as above-described in which a porous shell mold forming the support for the green body loses its structural strength during the nitriding of the silicon metal particles so that the mold can be removed from the article after nitriding without damage to the article.